Plasmon tomography

ABSTRACT

Plasmon energy is produced by exciting a plasmon resonance at least one excitation position on a first surface of a first material, and the plasmon energy is detected at at least one measurement position on the first surface after the plasmon energy has propagated from the at least one excitation position to the at least one measurement position. An attenuation of plasmon energy is determined along a plurality of paths between the at least one excitation position and the at least one measurement position, and relative distances between the first surface and a second surface of a second material are determined at a plurality of points on at least one of the surfaces based on the determined attenuation of plasmon energy along the plurality of paths.

For purposes of the USPTO extra-statutory requirements, the presentapplication constitutes a continuation of U.S. patent application Ser.No. 11/355,918, entitled PLASMON TOMOGRAPHY, naming Roderick A. Hyde asinventor, filed 16 Feb. 2006 now U.S. Pat. No. 7,466,420, which iscurrently, or is an application of which a currently application isentitled to the benefit of the filing date.

For purposes of the USPTO extra-statutory requirements, the presentapplication constitutes a continuation of U.S. patent application Ser.No. 11/402,305, entitled PLASMON TOMOGRAPHY, naming Roderick A. Hyde asinventor, filed 11 Apr. 2006 now U.S. No. 7,463,359, which is currently,or is an application of which a currently application is entitled to thebenefit of the filing date.

For purposes of the USPTO extra-statutory requirements, the presentapplication constitutes a continuation of U.S. patent application Ser.No. 12/287,927, entitled PLASMON TOMOGRAPHY, naming Roderick A. Hyde asinventor, filed 14 Oct. 2008 now U.S. Pat. No. 7,859,676, which iscurrently, or is an application of which a currently application isentitled to the benefit of the filing date.

TECHNICAL FIELD

This description relates, in general, to plasmon tomography.

BACKGROUND

Surface plasmon resonances (“plasmons”) can be excited at the interfaceof materials having different dielectric properties. Plasmons aredescribed generally in C. Kittel, “Introduction to Solid State Physics,”Wiley, 1995, which is incorporated herein by reference.

SUMMARY

According to one general aspect, a method includes producing plasmonenergy by exciting a plasmon resonance at least one excitation positionon a first surface of a first material and detecting the plasmon energyat least one measurement position on the first surface after the plasmonenergy has propagated from the at least one excitation position to theat least one measurement position. An attenuation of plasmon energy isdetermined along a plurality of paths between the at least oneexcitation position and the at least one measurement position, andrelative distances between the first surface and a second surface of asecond material are determined at a plurality of points on at least oneof the surfaces based on the determined attenuation of plasmon energyalong the plurality of paths.

Implementations may include one or more of the following features. Forexample, the method can further include determining absolute distancesbetween the first surface and the second surface at the plurality ofpoints based on the relative distances and on a known distance betweenthe first surface and the second surface at one of the points. The firstsurface can include a conductive layer. The first surface can define apart of a material that includes a photonic crystal.

The method can further include detecting plasmon energy at a pluralityof measurement positions along a periphery of the first surface. Themethod can further include exciting plasmon resonances at a plurality ofexcitation positions along a periphery of the first surface and/ordetecting plasmon energy at a plurality of measurement positions along aperiphery of the first surface.

Exciting a plasmon resonance can include providing optical energy to thefirst surface, and providing optical energy to the first surface caninclude illuminating at least a portion of the first surface with laserlight. Exciting a plasmon resonance can also include providing acoherent beam of electromagnetic radiation to the first surface.

At least one of the first or second surfaces can define a portion of amask and the other of the first or second surfaces can define a portionof a substrate. The mask can include a plurality of plasmon guides onthe first surface, and the plasmon guides can define the plurality ofpaths on the first surface. The plurality of plasmon guides can bedisposed substantially parallel to one another on the first surface. Themethod can further include exciting plasmon resonances at excitationpositions substantially located at first ends of each of the pluralityof plasmon guides and detecting plasmon energy at measurement positionssubstantially located at second ends of each of the plurality of plasmonguides.

The method can further include providing the first material having thefirst surface and providing the second material having the secondsurface facing the first surface. The first surface can be a patternedsurface, and the second material can include a polymer, and the methodcan further include heating the second material above a polymer-glasstransition temperature until a pattern corresponding to the patternedsurface of the first surface is created in the second material andcooling the second material below the polymer-glass transitiontemperature.

The method can further include altering the first or second surfaceafter determining relative distances between the first surface and thesecond surface. For example, plasmon energy can be produced by excitinga plasmon resonance at least one excitation position on the firstsurface after altering the first or second surface, and then, afteraltering the first or second surface, the plasmon energy can be detectedat least one measurement position on the first surface after the plasmonenergy has propagated from the at least one excitation position to theat least one measurement position. After altering the first or secondsurface, an attenuation of plasmon energy along a plurality of pathsbetween the at least one excitation position and the at least onemeasurement position can be determined and relative distances betweenthe first surface and the second surface can be determined at aplurality of points on at least one of the surfaces after altering thefirst or second surface based on the determined attenuation of plasmonenergy along the plurality of paths. Altering the first or secondsurface can include moving a micro-electro-mechanical structure on thealtered surface, moving a structure across the altered surface, orcatalyzing a reaction between materials of the first or second surfaceand another material.

In another general aspect, a method includes producing plasmon energy byexciting a plasmon resonance at least one excitation position on a firstsurface of a first material facing a second surface of a second materialand detecting an amount of plasmon energy at a measurement position onthe first surface after the plasmon energy has propagated from theexcitation position to the measurement position. A relative positionbetween the first and second surfaces is adjusted based on the amount ofplasmon energy detected at the measurement position.

Implementations may include one or more of the following features. Forexample, the second material can include a semiconductor material andthe first material can include a patterned mask. The method can furtherinclude providing the first material having the first surface andproviding the second material having the second surface facing the firstsurface. The method can include producing plasmon energy by exciting aplasmon resonance at the at least one excitation position on the firstsurface, detecting an amount of plasmon energy at the measurementposition on the first surface after the plasmon energy has propagatedfrom the excitation position to the measurement position, and adjustinga relative position between the first and second surfaces based on theamount of plasmon energy detected at the measurement position until theamount of plasmon energy detected at the measurement position issubstantially equal to a desired amount of plasmon energy.

The first surface can include a first deformity, and the second surfacecan include a second deformity. For example, the first deformity and thesecond deformity can be protrusions from the surfaces. The first andsecond deformities can be aligned along a direction substantiallyperpendicular to the first and second surfaces when the measured amountof plasmon energy is substantially equal to the desired amount ofplasmon energy.

According to another general aspect, an apparatus includes positioningstructures configured to align a first surface of a first material witha second surface of a second material, an optical energy source, adetector, and a processor. The source is alignable to provideelectromagnetic radiation at a frequency responsive to excite a plasmonresonance at at least one excitation position on a first surface of thefirst material. The detector is configured to produce a signalcorresponding to excited plasmon energy at least one measurementposition on the first surface spatially separated from the at least oneexcitation position. The processor is responsive to the signalcorresponding to excited plasmon energy at least one measurementposition and configured to determine at least one separation distancebetween the first material and the second material.

Implementations may include one or more of the following features. Forexample, the processor can be further configured to determine anattenuation of plasmon energy along a path between the at least oneexcitation position and the at least one measurement position and can beconfigured to determine at least one separation distance between thefirst surface and the second surface based at least in part on thedetermined attenuation of plasmon energy along the path. The processorcan also be configured to determine an attenuation of plasmon energyalong a plurality of paths between the at least one excitation positionand the at least one measurement position and an be configured todetermine at least one separation distance between the first surface andthe second surface based at least in part on the determined attenuationof plasmon energy along the plurality of paths.

The optical source can be a laser. The first surface can include aconductive layer and/or can define a part of a material comprising aphotonic crystal. The optical energy source can be configured to exciteplasmon resonances at a plurality of excitation positions along aperiphery of the first surface. The detector can be further configuredto produce signals corresponding to excited plasmon energy at aplurality of measurement positions along a periphery of the firstsurface spatially separated from the at least one excitation position.At least one of the first or second surfaces can define a portion of amask, and the other of the first or second surfaces can define a portionof a substrate. The mask can include a plurality of plasmon guides onthe first surface and the plasmon guides can define the plurality ofpaths on the first surface. The plurality of plasmon guides can bedisposed substantially parallel to one another on the first surface. Theoptical energy source can be further configured to excite plasmonresonances at excitation positions substantially located at first endsof each of the plurality of plasmon guides; and the detector can beconfigured to produce signals corresponding to excited plasmon energy atmeasurement positions substantially located at second ends of each ofthe plurality of plasmon guides.

The first surface can be a patterned surface, and the second materialcan include a polymer, and the apparatus can also include a heat sourceconfigured to heat the second material above a polymer-glass transitiontemperature until a pattern corresponding to the patterned surface ofthe first surface is created in the second material. The detector caninclude a coupler, which can include, e.g., a diffraction grating,adapted for coupling plasmon energy at the measurement position into anelectromagnetic wave.

In another general aspect, an apparatus includes positioning structuresconfigured to align a first surface of a first material with a secondsurface of a second material, an optical energy source, and a detector.The source is alignable to provide electromagnetic radiation at afrequency responsive to excite a plasmon resonance at least oneexcitation position on a first surface of the first material. Thedetector is configured to produce a signal corresponding to excitedplasmon energy at least one measurement position on the first surfacespatially separated from the at least one excitation position. And thepositioning structures are configured to adjust a relative positionbetween the first and second surfaces in response to the signal.

Implementations may include one or more of the following features. Forexample, the positioning structures can include a movable stageconfigured to align the first surface with the second surface, and theapparatus can further include a processor configured to process thesignal corresponding to excited plasmon energy to provide a signal tothe movable stage to move the first or second surfaces into an alignmentposition with the other of the first or second surface.

The second material can include a semiconductor material and/or thefirst material can include a patterned mask. The first surface caninclude a first deformity and the second surface can include a seconddeformity. The first deformity and the second deformity can beprotrusions from the surfaces. The detector can be configured to producea signal corresponding to an amount of excited plasmon energy at the atleast one measurement position on the first surface, and the positioningstructures can be configured to align the first deformity and the seconddeformity along a direction substantially perpendicular to the firstwith second surfaces when the detected amount of plasmon energy issubstantially equal to a desired amount of plasmon energy.

The detector can include a coupler adapted for coupling plasmon energyat the measurement position into an electromagnetic wave. The couplercan include a diffraction grating.

In another general aspect, an article includes a machine-accessiblemedium that stores executable instructions that cause electricalcircuitry to acquire data about an attenuation of plasmon energy along aplurality of paths between the at least one plasmon excitation positionon a first surface of a first material facing a second surface of asecond material and the at least one measurement position on the firstsurface and determine relative distances between the first surface and asecond surface of a second material at a plurality of points on at leastone of the surfaces based on the determined attenuation of plasmonenergy along the plurality of paths.

Implementations may include one or more of the following features. Forexample, the instructions can further cause the electrical circuitry toacquire data about a known distance between the first surface and thesecond surface at least one point on the first surface and to determineabsolute distances between the first surface and the second surface atthe plurality of points based on the relative distances and on the atleast one point on the first surface. The instructions can further causethe electrical circuitry to generate a control signal to whichpositioning structures respond by moving the first or second surfacerelative to the other surface.

In another general aspect, an article includes a machine-accessiblemedium that stores executable instructions that cause electricalcircuitry to acquire data about an amount of plasmon energy at ameasurement position on a first surface facing a second surfaceseparated from a measurement position from which the plasmon energy haspropagated, to compare the amount of plasmon energy to a predeterminedamount, and to generate a control signal to which positioning structuresrespond by moving the first or second surface relative to the othersurface.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features will beapparent from the description and drawings, and from the claims.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

DESCRIPTION OF DRAWINGS

FIG. 1 is schematic perspective view of a system for creating an imageof a surface using surface plasmon tomography.

FIG. 2 is schematic side view of an object having a surface upon which asurface plasmon resonance can be excited, along with a schematicrepresentation of the amplitude of the evanescent fields of the surfaceplasmon resonance.

FIG. 3 is schematic side view of an object having a surface upon which asurface plasmon resonance can be excited in close proximity to thesurface of another object, along with a schematic representation of theamplitude of the evanescent fields of the surface plasmon resonance.

FIG. 4 is a schematic side view of a system for exciting a surfaceplasmon resonance at a first position on the surface of an object andfor detecting energy in the surface plasmon resonance at anotherposition on the surface.

FIG. 5A is a schematic top view of a surface having several guides forguiding a surface plasmon resonance.

FIG. 5B is a schematic side view of a surface having several guides forguiding a surface plasmon resonance.

FIG. 6 is a schematic side view of an object having a surface upon whicha surface plasmon resonance can be excited in close proximity to anobject having a surface that can be altered.

FIG. 7 is a schematic side view of an object having a surface that canbe altered and upon which a surface plasmon resonance can be excited.

FIG. 8 is a schematic side view of an object having a surface upon whicha surface plasmon resonance can be excited and having alignment guidesin close proximity to an object having a surface with complementaryalignment guides.

FIG. 9A is a schematic side view of a mask in close proximity to analterable object.

FIG. 9B is a schematic side view of a mask in close proximity to analterable object after the object has been altered.

FIG. 10 is a flow diagram illustrating a method of determining relativedistances between two surfaces in accordance with some of theembodiments.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented here.

One or more implementations are described below. It should be noted thatthese implementations are exemplary and are intended to be illustrativerather than limiting. It is impossible to include all of possibleimplementations and contexts of the invention in this disclosure.

FIG. 1 is a schematic perspective view of a system 100 for determiningdistances between two surfaces and for creating an image of a surfaceusing surface plasmon tomography. An object 102 having a surface 104 tobe imaged is placed in close proximity to the surface 108 of anotherobject 106. Positioning structures 110 position the objects 102 and 106relative to each other, such that the surfaces 104 and 108 are in closeproximity to each other. The positioning structures can be staticspacers. For example, the positioning structures 110 can be structureshaving a predetermined height that are deposited or epitaxially grown onone of the surfaces 104 or 108 or, when one or both surfaces 104 or 110are rough the dedicated spacers can be omitted and the positioningstructures 110 can be portions of the surfaces that rise above otherportions of the surfaces and contact the opposite surface. Thepositioning structures 110 can also be moveable structures that canadjust dynamically the distance between surfaces 104 and 110. Forexample, the positioning structures 110 can be piezoelectric pillarsthat can change independently the distance between surfaces 104 and 108at different positions on the surfaces. The positioning structures 110also can be part of an x-y-z stage that can move either object 102 orobject 106, such that surfaces 104 and 108 are moved relative to eachother, either parallel or perpendicular to the surfaces.

The object 106 can include two layers 120 and 122 having differentdielectric constants, so that a surface plasmon resonance can be excitedat the interface between the two layers. To support a surface plasmonresonance, the real parts of the dielectric constants of the two layershave opposite signs at a particular excitation frequency. For example,the layer 120 can be an insulator or a semiconductor layer with adielectric constant having a positive real part, and the layer 122 canbe a thin conductive film (e.g., a gold or silver film) with adielectric constant having a negative real part.

A source of optical energy 130 can direct optical energy to theinterface between layers 120 and 122 to excite a surface plasmonresonance at an excitation position 132 on the surface 108 of the object106. The source 130 can be a source of coherent electromagnetic energy,e.g., a laser that generates electromagnetic waves having a frequencythat resonates with the surface plasmon resonance. The optical energycan be directed from the bottom of the layer 120 through layer 120 tothe interface between layers 120 and 122 when the layer is transparentto the optical energy. Alternatively, the source 120 can be positionedabove the object 106 and shined directly onto the surface 108, with thebeam path of the optical energy passing either between objects 106 and102 or through object 102. The beam path of the optical energy also canpass through the object 102 when the object 102 is transparent to theoptical energy. In still another implementation, the light source 130can be located on or within the object 106 and can energized to shineoptical energy toward the interface between layers 120 and 122. Forexample, the source 130 can include one or more light emitting diodes(LEDs) or semiconductor lasers fabricated within layers of the object106, and the light output from the LEDs or semiconductor lasers can bedirected to the interface of the layers 120 and 122 to excite a surfaceplasmon resonance.

When the surface plasmon resonance is excited at the excitation position132, energy in the resonance can travel on the surface 108 to adetection position 134 at which an amount of energy in the resonance canbe detected. For example, a coupler 136 at the detection position cancouple energy in the surface plasmon resonance into optical energy thatcan be transported in a waveguide (e.g., an optical fiber) to an opticalenergy detector 138 that detects an optical signal proportional theplasmon energy at the detection position 134. The output of the detector138 can be fed into a processor 140 and/or stored in a memory 142 andused to determine distances between surfaces 104 and 104 and/or tocreate an image of the surface 104 or 108, as explained in more detailbelow.

FIG. 2 is schematic side view of an object 200 having a surface 202 uponwhich a surface plasmon resonance can be excited, along with a schematicrepresentation 250 of the amplitude of the evanescent fields of thesurface plasmon resonance. The object 200 has two materials 204 and 206with dielectric constants having real parts with different signs, andthe plasmon resonance is created at the interface 208 between the twomaterials. For example, one material 206 can be a polymer, and the othermaterial 204 can be a thin conductive layer. One material can alsoinclude a photonic crystal (e.g., a vertical stack of alternating layersof material having different indices of refraction that). At theinterface 208 between the two materials the amplitude of the plasmonfield is greatest, and the field decays approximately exponentially asthe field penetrates into the material.

Although the layer 204 is described as a conductive layer in theexemplary implementation of FIG. 1, it is not necessary for the layer204 to be conductive for plasmons to be excited at the interface 208between layers 204 and 206. Plasmons may occur in other configurations.For example, if the real parts of the dielectric constants of layers 204and 206 have opposite signs at the interface 208, plasmons can beproduced and one skilled in the art may find a number of configurationsand material configurations that establish these conditions.

In one embodiment, the layer 204 may include vanadium dioxide, which isknown to undergo an insulator-to-metal or semiconductor-to-metal phasetransition at a certain temperature, as described in R. Lopez, L. A.Boatner, T. E. Haynes, L. C. Feldman, and R. F. Haglund, Jr., “Synthesisand characterization of size-controlled vanadium dioxide nanocrystals ina fused silica matrix,” Journal of Applied Physics, Volume 92, Number 7,Oct. 1, 2002, which is incorporated herein by reference. Byincorporating vanadium dioxide into the structure, the ability toproduce plasmons could be switched on or off depending on thetemperature of the material.

If a layer 204 is thinner than the penetration depth of the plasmonfield (e.g., the depth in the material at which the amplitude of theplasmon field is reduced by 1/e) then an appreciable amplitude of theplasmon field can leak out of the layer 204. For example, when a surfaceplasmon resonance is excited by coherent radiation having a wavelengthof about 1 μm, the 1/e depth of the evanescent plasmon field in a goldlayer is on the order of a few hundred nm. The penetration depth of thefield in a material is determined by the imaginary part of thematerial's dielectric constant, which, in turn, depends on theelectromagnetic properties of the material and the wavelength of theradiation. The penetration depth generally is greater for longerwavelength excitation radiation. Thus, the amplitude of the plasmonfield in the dielectric layer 206 can be represented by a decayingexponential curve 252, while the amplitude of the plasmon field in layer204 can be represented by the decaying exponential curve 254. Outside ofthe layer 204, the amplitude of the plasmon field can be represented bya third decaying exponential curve 256.

FIG. 3 is schematic side view of an object 200 having a surface uponwhich a surface 202 plasmon resonance can be excited in close proximityto the surface 302 of another object 300, along with a schematicrepresentation 350 of the amplitude of the evanescent fields of thesurface plasmon resonance. As shown in FIG. 3, the evanescent field ofthe surface plasmon resonance includes a portion 256 that extendsoutside of the layer 204 into the gap between the surfaces 302 and 202of the objects and a portion 358 that extends into the object 300.Because the imaginary part of the dielectric constant of the materialsdetermines the penetration depth of the surface plasmon field and alsothe dissipation of energy in the plasmon resonance as the resonancetravels parallel to the interface 208, the presence of differentmaterials close to the interface can affect the degree to which plasmonenergy is attenuated as the resonance travels parallel to the interface.By measuring plasmon energy attenuation as plasmons travel parallel tothe interface along different paths, relative distances between surfaces202 and 302 can be determined, and a profile of surface 302 and/or 202can be generated.

Referring again to FIG. 1, plasmons can be excited at multiple positions132 on the surface 108, and then the energy of the plasmons can bedetected at a detection location on the surface. Plasmon energy can alsobe detected at multiple different detection positions 134 on the surfacewhen the detected plasmon energy travels along different paths from oneor more excitation positions 132 to the detection positions 134. Datacorresponding to the energy received at the detection position 132 andthe path traveled by the plasmon from the excitation positions 132 tothe detection positions 134 when the plasmons travel along differentpaths can be stored in the memory 142. The data then can be deconvolvedby the processor 142 to determine generate an image of surface 108 or104. Although many deconvolution techniques and processes are known,some are described in U.S. Pat. No. 4,063,549 and in U.S. Pat. No.4,646,256.

In one implementation, when only object 106 is present, plasmon energycan be detected at multiple detection positions 134 after plasmonresonances having approximately the same initial energy are excited atmultiple excitation positions 132. Data concerning an amount of plasmonenergy detected at the detection positions 134 and the path traveled bythe plasmon from the excitation positions to the detection positions areused to determine an amount of attenuation along each path. Then,because different thicknesses of the surface layer 122 attenuate theplasmon energy by different amounts, information about the amount ofattenuation along each path can be deconvolved to create an image of therelative thickness in the z-direction of the surface layer 122 as afunction of position on the surface 108 in the x- and y-directions. Ifthe absolute thickness of the surface layer 122 is known at any oneposition, then this information can be combined with knowledge of therelative thicknesses at different positions on the surface 108 todetermine the absolute thicknesses of the surface layer 122 at differentpositions in the x- and y-directions on the surface 108.

In another implementation, when the surface 104 of object 102 is inclose proximity to the surface 108 of object 106, measurements ofplasmon energy attenuation can be used to determine a profile of thesurface 106. The thickness of the surface layer 122 can be assumed to beuniform, and the surface 108 can be assumed to be flat. When surfaceplasmons are excited at excitation positions 132 and travel to detectionpositions 134, the degree to which the plasmon energy is attenuated asthe plasmon travels along a path from the excitation position to thedetection position will depend on the distance between surfaces 108 and104, and, therefore, how far the evanescent plasmon field penetratesinto the object 102 as the plasmon travels along the path. Thus, dataconcerning an amount of plasmon energy detected at detection positions134 and the paths traveled by the plasmon from excitation positions 132to detection positions 134 can be used to determine an amount ofattenuation along each path, which information can be deconvolved todetermine a relative distances in the z-direction between surfaces 104and 108 as a function of position on the surface 108 in the x- andy-directions, i.e., z(x, y). An absolute distance between surfaces 104and 108 can be determined, for example, from the height of a positioningstructure 110 located between surfaces 104 and 108.

In another implementation, baseline measurements can be made on thesurface 108 before surface 104 is brought into close proximity withsurface 108 and the surface 104 is profiled. For example, without thepresence of object 102, surface plasmons can be excited and detected onthe surface 108, and information about the amount of attenuation alongeach path can be deconvolved to create an image of the relativethickness of the surface layer 122 as a function of x-y position on thesurface 108. These data can be stored as calibration data in memory 142and used to calibrate measurements used to profile the surface 104, whensurface is in close proximity to surface 108. For example, afterobtaining the calibration data and bringing surface 108 into closeproximity with surface 104, surface plasmons can be excited and detectedon the surface 108 and information about the amount of attenuation alongpaths that are similar to paths used to obtain the calibration data canbe compared with the calibration data. For example, if the amount ofattenuation along a particular path changes substantially when thesurface 108 is brought close to surface 104, then the surfaces are quiteclose together along that path. However if the amount of attenuationalong a different path changes very little when the surface 108 isbrought close to surface 104, then the surfaces are relatively far apartalong that different path. Moreover, the calibration data can be used toremove effects caused by a non-uniform thickness of layer, whengenerating a profile of surface 104 from the information about theattenuation of plasmon energy along multiple paths on surface 108 whensurface 104 is in close proximity to surface 108.

FIG. 4 is a schematic side view of a system for exciting a surfaceplasmon resonance at a first position on the surface of an object andfor detecting energy in the surface plasmon resonance at anotherposition on the surface. The object 400 has a layer of material 402 andanother layer of material 404, and the materials have dielectricconstants with real parts having opposite signs. Thus, a plasmonresonance can be excited at the interface 406 between the two layers ofmaterial. To couple energy to the surface plasmon resonance, opticalenergy can be shined through one of the layer onto the interface, asshown in FIG. 1.

In another implementation, a laser 410 can generate optical energy thatis directed toward the upper layer 404, either in a direct path from thelaser or through a waveguide 412 (e.g., an optical fiber). The opticalenergy can be coupled into the object 400 and to the interface 406through a coupler 420 on the surface of the object. For example, thecoupler 420 can direct light toward a Bragg grating 422 that scattersthe optical energy into the layer 404 to the interface 406 where aplasmon resonance is excited.

Plasmon energy can be coupled out of the object in a similar manner. Forexample, plasmon energy can be scattered by a Bragg grating 432 andconverted into optical energy that is picked up by a coupler 430 thatdirects the optical energy into a waveguide 434 (e.g., an opticalfiber). The waveguide 434 can transport the optical energy to a detector436 that measures that amount of optical energy.

Other methods of coupling energy between electromagnetic waves andplasmons are possible, some of which are described in W. L. Barnes, A.Dereux, and T. W. Ebbesen, “Surface plasmon subwavelength optics,”Nature, Volume 424, Aug. 14, 2003, 824-830, which is incorporated hereinby reference. These methods include and are not limited to couplingthrough a prism, coupling by scattering from a topological defect on thesurface on which the plasmon is to be generated, and coupling through aperiodic corrugation in the surface on which the plasmon is to begenerated.

FIGS. 5A and 5B are schematic top and side views, respectively, of asurface having several guides for guiding a surface plasmon resonance.The guides 502 can be formed by a first material 504 that overlays asecond material 506, where the first and second materials havedielectric constants with opposite signs to their real parts. Forexample, the second material 506 may be a semiconductor, and the firstmaterial 504 may be a metallization layer deposited, on the secondmaterial. When a plasmon resonance is excited at the interface of thefirst and second materials, the plasmon can travel parallel to theinterface and can be guided along the path of a guide 502. Thus, theguides 502 provide a predictable path for the plasmons to travel from anexcitation position to a detection position.

In one implementation, the guides 502 can cross the surface from oneperimeter position of the surface to another perimeter position. Asurface plasmon resonance can excited at a position 510 at one perimeterposition, and the energy in the plasmon can be detected at anotherposition 512 at another perimeter position on the surface.

The guides 502 can be located on a mask that is placed in closeproximity to a semiconductor wafer, so that a pattern in the mask can betransferred into the wafer. In one implementation, the guides 502 canform part of the pattern in the mask. By collecting and deconvolvinginformation about the attenuation of plasmon energy as plasmons travelalong guides from an excitation position to a detection position, thedistance between the mask and the semiconductor can be determined acrossthe surface of the mask and the semiconductor wafer. If the distancedoes not conform to a desired distance at certain locations on thesurface, the distance can be adjusted a one or more positions, and thenthe distance can be measured again.

FIG. 6 is a schematic side view of an object 600 having a surface uponwhich a surface plasmon resonance can be excited in close proximity toan object 650 having a surface that can be altered. In oneimplementation, the object 650 can have a surface 652 with one or moreobjects 654 that can be moved or altered. For example, the object can bea micro-electromechanical structure (e.g., a mirror or a carbonnanotube) whose position can be moved when a signal is applied to thestructure. For example, the structure can be moved from a first position660 to a second position 662 when the signal is applied to thestructure.

One or both of the objects 600 and 650 can include an interface 610between two materials having dielectric constants with real parts havingopposite signs, and a surface plasmon resonance can be excited at theinterface. By collecting and deconvolving information about theattenuation of plasmon energy as plasmons travel along the interface 610following multiple paths from excitation positions to detectionpositions, the distance between the facing surfaces of objects 600 and650 can be determined at multiple points on the surfaces. Measurement ofthe distance between the surfaces can be used to determine whether themoveable objects 654 have moved and to image the surface 652 includingthe moveable objects before and after movement of the objects 654. Inanother implementation, the moveable objects 654 can be products ofphysical, chemical, and/or biological reactions, and movement of theobject 654 can correspond to the occurrence of a reaction. For example,a biological protein may be assembled on the surface 652, andmeasurement of the distance between facing surfaces of the objects 600and 650 can be used to determine whether the reaction has occurred, andto image the surface 652 including the reaction products before andafter the reaction.

FIG. 7 is a schematic side view of an object 700 having a surface 702that can be altered and upon which a surface plasmon resonance can beexcited. The object 700 has two materials 704 and 706 with dielectricconstants having real parts with different signs, and the plasmonresonance is created at the interface 708 between the two materials. Forexample, one material 706 can be a polymer, and the other material 704can be a thin conductive layer. At the interface 708 between the twomaterials the amplitude of the plasmon field is greatest, and the fielddecays approximately exponentially as the field penetrates into thematerial. Plasmons can be excited at excitation positions on the surface702 of the object and detected at detection positions, and by recordingmeasurements of the attenuation of plasmon energy as the plasmons travelover multiple paths from excitation positions to detection positions,baseline measurements on the object can be made and recorded. Then,after the baseline measurements have been recorded, the surface 702 canbe altered. For example, material 710 can be deposited on the surface702, or a chemical or biological reaction can occur at the surface,which results in material 710 adhering to surface 702 or in analteration of the surface. After alteration of the surface, plasmonsagain can be excited at excitation positions on the surface 702 anddetected at detection positions. By measuring the attenuation of plasmonenergy as the plasmons travel over multiple paths on the altered surfaceand comparing the measurements with the recorded baseline measurements,a profile of the altered surface as it compares with the originalsurface can be generated.

FIG. 8 is a schematic side view of an object 800 having a surface 802upon which a surface plasmon resonance can be excited and havingalignment guides 804 in close proximity to another object 850 having asurface 852 with complementary alignment guides 854. An optical energysource 810 can provide optical energy to an interface 812 between twodifferent materials within object 800 to excite a plasmon resonance atan excitation position in the object 800. The plasmon energy can betransported along the interface to a detection position 816, where acoupler 818 couples the plasmon energy into optical energy that isguided to a detector 820. The detector 802 produces a signal proportionto the plasmon energy at the detection position, and information in thesignal is processed by a processor 822.

Object 850 can be moved relative to object 800 by positioning structures860. When the object is moved into a position 870 in which its alignmentguides 804 are aligned with the alignment guides 854 of the object 850,such that a separation between alignment guides 804 and 854 isminimized, the attenuation of plasmon energy as the plasmon travels fromthe excitation position 814 to the detection position 816 is eitherminimized or maximized. When the object 850 is moved into a position 872in which the guides 804 and 854 are not aligned, the attenuation ofplasmon energy will not take on an extreme value. Thus, objects 800 and850 can be aligned by continuously or repeatedly exciting a plasmon atan excitation position 814 while detecting the plasmon energy at adetection position 816 and monitoring the detected amount of plasmonenergy. When the amount of plasmon energy detected reaches an extremum(i.e., either a maximum or a minimum), the objects are aligned.

FIGS. 9A and 9B are schematic side views of a mask 900 in closeproximity to an alterable object 950 that can be deformed into a newshape 960. The mask has a surface 902 that includes a profile that canbe transferred to the alterable object. Material 904 at the surface 902has a dielectric constant with a real part that is either positive ornegative. A layer of material 906 under the surface material 904 has adielectric constant with a real part that has a sign that is opposite tothe sign of the surface layer's dielectric constant. For example, layer906 can be a transparent insulator or a semiconductor layer, and layer904 can be a metallization layer. Thus, a plasmon can be excited at theinterface between layers 904 and 906.

The surface 902 of mask 900 is in close proximity to the surface 952 ofthe alterable object 950. For example, positioning structures 960 canmaintain a gap between the surfaces 902 and 952, as shown in FIG. 9A. Byexciting plasmon resonances at excitation positions on the surface 952and detecting plasmon energy at detection positions on the surface,measurements of plasmon energy attenuation can be made as the plasmonstraverse different paths on the surface. Information about the plasmonenergy attenuation over the different paths can be deconvolved togenerate an image of the profile of the mask surface 952 and of thedistance between the mask and the surface 902. This information can bestored as baseline information.

As shown in FIG. 9B, the object 960 can include a material 954 (e.g., apolymer material) that can be deformed. For example, the material 954can be heated above a polymer-glass transition temperature, such thatthe material flows and takes on a complementary shape to the profile ofthe mask surface 902. After deforming the object 960 plasmon resonancesagain can be excited at excitation positions on the surface 952 and theplasmon energy can be detected at detection positions on the surface.Measurements of plasmon energy attenuation can be made as the plasmonstraverse different paths on the surface. Information about the plasmonenergy attenuation over the different paths can be deconvolved andcompared to the baseline information recorded before the object 950 wasdeformed to generate an image of the surface 962 of the deformed object960. The material 954 can then be cooled, and the deformed object 960can be separated from the mask 900.

FIG. 10 is a flow diagram illustrating a method of determining relativedistances between two surfaces in accordance with some of theembodiments. The method generally begins at block 1002, whereuponplasmon energy is produced by exciting a plasmon resonance at least oneexcitation position on a first surface of a first material. The plasmonenergy can be produced by providing optical energy to the first surface(e.g., by illuminating at least a portion of the first surface withlaser light or by providing a coherent beam of electromagnetic radiationto the first surface). The first material can include a conductive layerand/or a photonic crystal.

At block 1010 the plasmon energy is detected at least one measurementposition on the first surface after the plasmon energy has propagatedfrom the at least one excitation position to the at least onemeasurement position. The excitation positions and/or measurementpositions can be located along a periphery of the first surface.

At block 1020 an attenuation of plasmon energy is determined along aplurality of paths between the at least one excitation position and theat least one measurement position. The first or second surface candefine a portion of a mask, and the other of the first or secondsurfaces can define a portion of a substrate. The mask can include aplurality of plasmon guides on the first surface and the plasmon guidescan define a plurality of paths on the first surface. The plurality ofplasmon guides can be disposed substantially parallel to one another onthe first surface.

At block 1030 relative distances are determined between the firstsurface and a second surface of a second material at a plurality ofpoints on at least one of the surfaces based on the determinedattenuation of plasmon energy along the plurality of paths.

At optional block 1040 absolute distances between the first surface andthe second surface at the plurality of points can be determined based onthe relative distances and on a known distance between the first surfaceand the second surface at one of the points.

At optional block 1000 the first material having the first surface canbe provided and the second material can be provided having the secondsurface facing the first surface.

At optional block 1050, when the first surface is a patterned surfaceand the second material includes a polymer, the second material can beheated above a polymer-glass transition temperature until a patterncorresponding to the patterned surface of the first surface is createdin the second material and then the second material can be cooled belowthe polymer-glass transition temperature.

At optional block 1060 the first or second surface can be altered afterdetermining relative distances between the first surface and the secondsurface. For example, a micro-electro-mechanical structure can be movedon the altered surface, a structure can be moved across the alteredsurface, or a reaction can be catalyzed between materials of the firstor second surface and another material.

In this disclosure, references to “optical” elements, components,processes, or other aspects, as well as references to “light” may alsorelate in this disclosure to so-called “near-visible” light such as thatin the near infrared, infra-red, far infrared and the near and farultra-violet spectrums. Moreover, many principles herein may be extendedto many spectra of electromagnetic radiation where the processing,components, or other factors do not preclude operation at suchfrequencies, including frequencies that may be outside ranges typicallyconsidered to be optical frequencies.

This detailed description sets forth various implementations of thedevices and/or processes via the use of block diagrams, diagrammaticrepresentations, and examples. Insofar as such block diagrams,diagrammatic representations, and examples contain one or more functionsand/or operations, it will be understood as notorious by those withinthe art that each function and/or operation within such block diagrams,diagrammatic representations, or examples can be implemented,individually and/or collectively, by a wide range of hardware,materials, components, or virtually any combination thereof.

Those having skill in the art will recognize that a typical opticalsystem generally includes one or more of a system housing or support,and may include electrical components, alignment features, one or moreinteraction devices, such as a touch pad or screen, control systemsincluding feedback loops and control motors (e.g., feedback for sensingpositions of optical elements (e.g., lens, filters, beam splitters, anddetectors); control motors for moving/distorting optical elements toprovide desired optical behavior). Such systems may include imageprocessing systems, image capture systems, photolithographic systems,scanning systems, or other systems employing optical, RF, IR, UV, X-rayor other focusing or refracting elements or processes.

In a general sense, those skilled in the art will recognize that thevarious aspects described herein which can be implemented, individuallyand/or collectively, by a wide range of hardware, software, firmware, orany combination thereof can be viewed as being composed of various typesof “electrical circuitry.” Consequently, as used herein “electricalcircuitry” includes, but is not limited to, electrical circuitry havingat least one discrete electrical circuit, electrical circuitry having atleast one integrated circuit, electrical circuitry having at least oneapplication specific integrated circuit, electrical circuitry forming ageneral purpose computing device configured by a computer program (e.g.,a general purpose computer configured by a computer program which atleast partially carries out processes and/or devices described herein,or a microprocessor configured by a computer program which at leastpartially carries out processes and/or devices described herein),electrical circuitry forming a memory device (e.g., forms of randomaccess memory), and electrical circuitry forming a communications device(e.g., a modem, communications switch, or optical-electrical equipment).

The herein described aspects depict different components containedwithin, or connected with, different other components. It is to beunderstood that such depicted architectures are merely exemplary, andthat in fact many other architectures can be implemented which achievethe same functionality. In a conceptual sense, any arrangement ofcomponents to achieve the same functionality is effectively “associated”such that the desired functionality is achieved. Hence, any twocomponents herein combined to achieve a particular functionality can beseen as “associated with” each other such that the desired functionalityis achieved, irrespective of architectures or intermedial components.Likewise, any two components so associated can also be viewed as being“operably connected,” or “operably coupled,” to each other to achievethe desired functionality, and any two components capable of being soassociated can also be viewed as being “operably couplable,” to eachother to achieve the desired functionality. Specific examples ofoperably couplable include but are not limited to physically mateableand/or physically interacting components and/or wirelessly interactableand/or wirelessly interacting components and/or electricallyinteractable and/or electrically interacting components.

In one or more various aspects, related systems include but are notlimited to circuitry and/or programming and/or electro-mechanicalcomponents for effecting the herein-referenced method aspects; thecircuitry and/or programming and/or electro-mechanical components can bevirtually any combination of hardware, software, firmware, and/orelectro-mechanical components configured to effect the herein-referencedmethod aspects depending upon the design choices of the system designerin light of the teachings herein. Some portions of the subject matterdescribed herein may be implemented via Application Specific IntegratedCircuits (ASICs), Field Programmable Gate Arrays (FPGAs), digital signalprocessors (DSPs), or other integrated formats. However, those skilledin the art will recognize that some aspects of the embodiments disclosedherein, in whole or in part, can be equivalently implemented in standardintegrated circuits, as one or more computer programs running on one ormore computers (e.g., as one or more programs running on one or morecomputer systems), as one or more programs running on one or moreprocessors (e.g., as one or more programs running on one or moremicroprocessors), as firmware, or as virtually, any combination thereof,and that designing the circuitry and/or writing the code for thesoftware and or firmware would be well within the skill of one of skillin the art in light of this disclosure. In addition, those skilled inthe art will appreciate that the mechanisms of the subject mattersubject matter described herein are capable of being distributed as amachine-readable program product in a variety of forms, and that anillustrative embodiment of the subject matter subject matter describedherein applies equally regardless of the particular type of signalbearing media used to actually carry out the distribution. Examples of asignal bearing media include, but are not limited to, the following:recordable type media such as floppy disks, hard disk drives, CD ROMs,digital tape, and computer memory; and transmission type media such asdigital and analog communication links using TDM or IP basedcommunication links (e.g., packet links).

While particular embodiments of the present invention have been shownand described, it will be understood by those skilled in the art that,based upon the teachings herein, changes and modifications may be madewithout departing from this invention and its broader aspects and,therefore, the appended claims encompass within their scope all suchchanges and modifications as are within the true spirit and scope ofthis invention. Furthermore, it is to be understood that the inventionis solely defined by the appended claims. It will be understood by thosewithin the art that, in general, terms used herein, and especially inthe appended claims (e.g., bodies of the appended claims) are generallyintended as “open” terms (e.g., the term “including” should beinterpreted as “including but not limited to,” the term “having” shouldbe interpreted as “having at least,” the term “includes” should beinterpreted as “includes but is not limited to,” “comprise” andvariations thereof, such as, “comprises” and “comprising” are to beconstrued in an open, inclusive sense, that is as “including, but notlimited to,” etc.). It will be further understood by those within theart that if a specific number of an introduced claim recitation isintended, such an intent will be explicitly recited in the claim, and inthe absence of such recitation no such intent is present. For example,as an aid to understanding, the following appended claims may containusage of the introductory phrases “at least one” and “one or more” tointroduce claim recitations. However, the use of such phrases should notbe construed to imply that the introduction of a claim recitation by theindefinite articles “a” or “an” limits any particular claim containingsuch introduced claim recitation to inventions containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should typically be interpreted to mean “atleast one” or “one or more”); the same holds true for the use ofdefinite articles used to introduce claim recitations. In addition, evenif a specific number of an introduced claim recitation is explicitlyrecited, those skilled in the art will recognize that such recitationshould typically be interpreted to mean at least the recited number(e.g., the bare recitation of “two recitations,” without othermodifiers, typically means at least two recitations, or two or morerecitations). Furthermore, in those instances where a conventionanalogous to “at least one of A, B, and C, etc.” is used, in generalsuch a construction is intended in the sense one having skill in the artwould understand the convention (e.g., “a system having at least one ofA, B, and C” would include but not be limited to systems that have Aalone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). In those instances where aconvention analogous to “at least one of A, B, or C, etc.” is used, ingeneral such a construction is intended in the sense one having skill inthe art would understand the convention (e.g., “a system having at leastone of A, B, or C” would include but not be limited to systems that haveA alone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.).

All of the U.S. patents, U.S. patent application publications, U.S.patent applications, foreign patents, foreign patent applications andnon-patent publications referred to in this specification and/or listedin any Application Data Sheet, are incorporated herein by reference, intheir entireties.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

1. A system comprising: positioning structures configured to align afirst surface and a second surface; a source configured to exciteplasmon energy at at least one excitation position on the first surface;a detector assembly configured to produce signals corresponding toreceived plasmon energy at a plurality of measurement positions on thefirst surface spatially separated from the at least one excitationposition by respective plasmon paths, wherein the plurality ofmeasurement positions correspond to a fixed relative position of thefirst and second surfaces; and a processor responsive to the producedsignals to determine at least one separation distance between the firstand second surfaces.
 2. The system of claim 1 wherein the processor isfurther responsive to the produced signals to create a topographical mapof the second surface.
 3. The system of claim 1 wherein the sourceincludes a laser.
 4. The system of claim 1 further comprising: awaveguide configured to direct energy from the source to the at leastone excitation position.
 5. The system of claim 1 further comprising: awaveguide configured to direct energy from at least one of the pluralityof measurement positions to the detector assembly.
 6. The system ofclaim 1 further comprising: one or more microelectromechanicalstructures positioned substantially between the first and secondsurfaces, the one or more microelectromechanical structures beingresponsive to signals to adjust at least one of the first and secondsurfaces.
 7. The system of claim 6 further comprising: a control systemoperably connected to provide the signals to the one or moremicroelectromechanical structures.
 8. The system of claim 1 wherein theprocessor is further responsive to signals to create an image of one ormore objects located substantially between the first and secondsurfaces.
 9. The system of claim 1 further comprising: a control systemoperably connected to the source configured to excite plasmon energy.10. The system of claim 9 further comprising: a touch pad receptive ofuser input and operably connected to the control system.
 11. The systemof claim 1 further comprising: a control system operably connected tothe detector assembly.
 12. The system of claim 1 further comprising: ascreen operably connected to the processor and configure to display thedetermined at least one separation distance between the first and secondsurfaces.
 13. The system of claim 1 further comprising: a control motoroperably connected to the positioning structures.
 14. The system ofclaim 13 further comprising: a control system operably connected to thecontrol motor.
 15. The system of claim 1 further comprising: a couplerlocated at the at least one excitation position on the first surface andconfigured to excite plasmon energy responsive to electromagneticenergy.
 16. The system of claim 15 wherein the coupler includes a prism.17. The system of claim 15 wherein the coupler includes a grating. 18.The system of claim 15 wherein the coupler includes a topologicaldefect.
 19. An apparatus comprising: circuitry configured to provideplasmon energy to at least one excitation position on a first surface;circuitry configured to receive a signal corresponding to detectedplasmon energy at at least one measurement position on the first surfaceafter the plasmon energy has propagated from the at least one excitationposition to the at least one measurement position; circuitry configuredto determine an attenuation of plasmon energy along a plurality ofdifferent paths on the first surface and between the at least oneexcitation position and the at least one measurement position; andcircuitry configured to determine relative distances between the firstsurface and a second surface at a plurality of points on at least one ofthe surfaces based on the determined attenuation of plasmon energy alongthe plurality of paths.
 20. The apparatus of claim 19 wherein thecircuitry configured to determine relative distances between the firstsurface and a second surface at a plurality of points is furtherconfigured to create an image of the second surface.
 21. The apparatusof claim 19 further comprising: circuitry configured to output thedetermined relative distances between the first surface and a secondsurface to a screen.
 22. The apparatus of claim 19 further comprising:circuitry configured to provide one or more signals to one or moremicroelectromechanical structures, wherein the one or moremicroelectromechanical structures are responsive to the one or moresignals to adjust at least one of the first and second surfaces.
 23. Amethod comprising: producing plasmon energy at at least one excitationposition on a first surface; detecting the plasmon energy at at leastone measurement position on the first surface after the plasmon energyhas propagated from the at least one excitation position to the at leastone measurement position; determining an attenuation of plasmon energyalong a plurality of different paths on the first surface and betweenthe at least one excitation position and the at least one measurementposition; and determining relative distances between the first surfaceand a second surface at a plurality of points on at least one of thesurfaces based on the determined attenuation of plasmon energy along theplurality of paths.